1. Field of the Invention
The present invention relates to new and useful improvements in two-stroke cycle gasoline engines and to new and useful improvements in exhaust valves for such engines. More particularly, the present invention provides a sliding exhaust valve which delays the opening of the exhaust port during the expansion stroke and, if desired, advances the closing of the exhaust port during the compression stroke while, at the same time, opening the exhaust port to permit proper blow down and allow scavenging of the combustion chamber.
2. Description of the Prior Art
It has been known in the past to provide speed-controlled exhaust valves which will remain partially closed at slow speeds of the engine, delaying communication between the combustion chamber and exhaust passage beyond the usual opening of the exhaust port by the piston, and move upward, fully exposing the exhaust passage to the combustion chamber through the exhaust port, at high engine speeds. Such valves, however, do not provide the advantages of longer expansion and compression strokes while also permitting maximum scavenging.
In the parent application, U.S. patent application Ser. No. 096,551, now allowed, a novel exhaust control valve is disclosed employing a linkage to the crankshaft which provides opening and closing of the exhaust passage during each cycle of the engine. This invention provides many distinct advantages, including an improved power stroke, more efficient and thorough combustion of fuel, and improved performance of downstream pollution control devices, such as catalytic converters, due to higher and more uniform exhaust temperatures. Although the invention of the parent application is believed to function quite well, applicant has found that further modifications to the basic concept are possible.
Accordingly, it is a primary object of the present invention to provide an exhaust control valve which provides an effective constriction of the exhaust passage when the valve is closed and provides minimal turbulent flow throughout its operation.
It is an additional object of the present invention to provide a sliding exhaust control valve drive mechanism which provides a direct and effective translation of the rotary motion of the crankshaft into the reciprocating motion of the valve element.
It is another object of the present invention to provide an exhaust control valve which is relatively simple in design, and provides reliable and straightforward operation, while avoiding short circuiting of combustible mixture.